DE69922419T2 - PROCESS FOR REDUCING SYNCHRONIZATION TIME DURING FURTHER - Google Patents

Description

Territory of invention

The The present invention relates to a method for carrying out a Synchronization of a mobile network device with a network controller a radio network area and a network control device for Carrying out this Process.

BACKGROUND THE INVENTION

One Mobile network consists of a variety of cells, each one are provided with one or more base stations. Is moving a mobile station from a first cell to a second cell, becomes a handover process (Handoff procedure), by the mobile station from the first cell (i.e., its base station) separated and with the second cell (i.e., the base station of the second Cell). A handover process is usually performed when the signal strength the current base station decreases and the signal strength of one adjacent cell greater than which is the current base station. It should be noted that in on CDMA ("Code Division Multiple Access ", Code division based systems usually have the signal-to-noise ratio SNR for the decision on one Handover process is used.

More accurate As said, the mobile station continuously measures the signal strength surrounding cells (i.e., base stations). The measurements will be carried out, if it does not send or receive (for example while TDMA ("Time Division Multiple Access ", Time-division multiplex) blocks, but can even while of sending or receiving. A base station controller (Base Station Controller, BSC) or a mobile services switching center Center ", MSC) collects these Measurements along with his knowledge of the quality of the existing linkage. If decided that will be a handover process required, the BSC or the MSC assigns the base station (BS) the new cell to prepare a channel, picks up the channel, which has been prepared, sends a message to the Mobile station telling her which channel to go to will check that the mobile station appears on this channel and then deactivates the old canal. The MSC may also be due to traffic congestion a handover process decide from mobile stations. In case it is a very congested one Cell gives, the can Mobile stations in the cell, which are also from other, adjacent Cells can be covered to reduce the burden of overloaded Cell to be instructed to a handover process.

Next This "hard" handover process, at the MS is switched from one channel to another It also has a handover process during which the MS has both Channels connected is. This becomes a "soft" handover process called and serves to provide a better voice quality during the Handover process, because during the "hard" handover process, there is a risk that the Connection for a short time is interrupted. Another type of handover process is the so-called "softer" handover process that takes place within performed the same cell becomes.

There the handover between two cells is not at a predetermined one geographical location, but depending on the signal strength is performed, the distance between the MS and the new BS is unknown. The reason for this is that the cell boundaries are not sharp but due shading, and the like are blurred. Furthermore, they can cell boundaries also change over time due to cell breathing.

Therefore after the handover, the distance between the MS and the new BS unknown. Due to the occurring between the MS and the BS Distance is therefore not known a propagation delay. It is but important for the base station to know the propagation delay, otherwise Interference, and the like may occur.

Especially is the propagation delay for one Synchronization between uplink and downlink connection important. For example, in GSM (Global System for Mobile Communications) the Communication between the mobile station and the base station in performed two different time slots. In particular, the transmission of Downlink transmission blocks three Time slots after transmission the uplink transmission blocks performed. The Time differences between the time slots are specified. Therefore, in the case of a large Distance between the MS and the BS the propagation delay of the uplink transmission blocks and the downlink transmission blocks become. Consequently, the MS must have a period earlier than transmit the time period determined only by the time slots.

The information about how much to send a burst earlier is transmitted to the MS by a signal TA (timing advance) generated by the BS or BSC corresponding to the current propagation delay, the value of TA corresponding to the to and fro ( "round trip") Value of the spread BS-MS-BS corresponds, ie twice the propagation delay. The value of TA is dynamic and changes with time. Its current value is sent to the MS within an information channel (more precisely, in the Layer 1 header of each SACCH, ie, Slow Associated Control Channel, or slower associated control channel.) The further the MS is away from the BS, the larger it is required TA.

Therefore is immediately after execution a handover process the propagation delay between The MS and the new BS are the largest, usually a handover process is performed at the boundary of the corresponding cell. However, this is to this Time the propagation delay too not known.

Therefore causes a wrong TA value, especially in the case of a large cell an interference. Although in CDMA networks the interference performance soon after completion of the handover process (because of a power control and the one described above soft handover process), this interference occurs with the handover process and significantly affects the communication quality. And not just the current connection between the current MS and the BS is affected by such interference, as well other connections experience interference because of a wrong one estimated propagation delay also the transmission is moved to an adjacent time slot, so that the over this Time slot executed Communication (between the BS and the other MSs) is affected.

It Please note that the propagation delay with regard to GSM has been described as an example, but this problem also in others Radio networks occurs.

The US 5349158 discloses a handover procedure initiation system for a mobile network having means for determining the distance of a mobile user from a cell base station based on propagation delay methods and means for measuring signal strength for determining the path of the mobile station.

The WO 98/15150 describes a method for determining the position a mobile station based on propagation delay measurements.

In In view of the above, it is to provide a good one Connection required that a correct propagation delay so early like possible is detected.

So far was a big one adapted filter for uses such a detection. The use of a customized Filters allows the detection of the propagation delay, although it is not known or uncertain at the beginning. however the matched filter must be set to have a minimal propagation delay (i.e., a delay of zero) and can detect a maximum propagation delay for the cell. That means a tremendous amount of different possible propagation delays must be considered. This requires a tremendous Hardware scale. Furthermore, for the same reason with a fairly long search time can be expected.

SUMMARY THE INVENTION

It is therefore an object of the invention, the above described disadvantages of the prior art, and to enable a fast detection of the propagation delay.

These Task is by a method of performing a synchronization a mobile network device with a network control device of existing radio network area after a handover process. The Method comprises the steps of detecting a source radio network area, from the handover process of the mobile network device in the existing radio network area, of determining a Start propagation delay value based on the detected source radio network area of the mobile station and looking for an actual one Propagation delay value by using one on the determined initial propagation delay value based search strategy.

Further The above object is achieved by a network controller an existing radio network area solved, with a detection device for detecting a source radio network area from which a handover a mobile network device in the existing radio network area carried out a determiner for determining an initial propagation delay value based on the detected source radio network area of the mobile station and a searching means for searching an actual propagation delay value by using a search strategy based on the particular one Start propagation delay value.

By the above method and the network control device can the correct propagation delay value be detected very quickly, since the values of the propagation delay of known, stored adjacent cells and for generating an initial value for the Search for the correct propagation delay can be used.

moreover is just a short matched filter (MF) for the search required after the correct propagation delay. Therefore the hardware extent can be reduced.

Further the search time is minimized because the most likely delay is first is searched for, a closed power control loop can be activated and the interference in the network is minimized, resulting in increased capacity of the network leads.

Further advantageous developments are defined in the dependent claims.

SUMMARY THE DRAWING

The Invention will be described below with reference to the accompanying Drawing closer described. Show it:

1 a radio network to which the present embodiment is applicable,

2 a flowchart illustrating a method of synchronization according to the embodiment,

3 a base station according to the embodiment,

4 the contents of a database 14 the base station according to the embodiment,

5 the contents of a database 14 ' the base station according to a modified embodiment, and

6a to 6e Examples of propagation delay search strategies used according to the embodiment and the modified embodiment.

DESCRIPTION THE PREFERRED EMBODIMENTS

in the The following will be a preferred embodiment of the invention described in more detail with reference to the accompanying drawings.

1 schematically shows a radio network consisting of a plurality of cells, to which the present invention can be applied. In this example, only four cells, CELL_1, CELL_2, CELL_3, and CELL_4, are shown. Each cell is divided into three sectors. Here, each sector represents an example of a radio network area. If the cells are not subdivided, a cell can also be a radio network area.

in the Following is a case where a handover of a mobile station (hereinafter referred to as MS) as an example of a mobile network device into the target sector CST. The source sector (that is, the sector from which the MS enters the target sector CST has been moved) is one of the adjacent sectors CS1 bis CS8.

In this network, for example, a handover operation is performed from a sector CS4 (as a source sector) located in cell CELL_2 to the target sector CST. This handover (HO) process is indicated by the dashed arrow in 1 displayed.

It must be noted that the cell boundaries are not as in 1 are sharp, but due to shading are blurred, and that they may even change over time due to cellular respiration. The phenomenon of so-called cell respiration is caused by changing transmission conditions due to weather conditions or changing loads in the cell.

As already described in the introductory part, becomes a handover process initiated, if the signal strength a connection between an MS and a base station (hereafter referred to as BS) drops below a certain level. Then it will be usually a handover into a cell (i.e., BS) with the largest signal strength. Therefore is the position of MS during the handover process and thus the correct propagation delay between the MS and the new OS immediately after the handover known.

According to this embodiment will correct the propagation delay through use a search strategy that uses an initial value, then through the implementation of iterations, gradually the actual propagation delay value is approximated.

Especially is a value based on the source cell or the initial value Source sector determined (or selected). That is, one known earlier Propagation value for an MS that does a handover from the same source cell or the same Source sector or target sector, is used as initial value for used the search.

The operation performed according to the present embodiment will be described with reference to FIG 2 shown flowchart described.

First, the source sector is detected in step S2. This may be performed such that the MS sends corresponding information after a connection was made between the new BS and the MS.

One another way of detecting the one handover process Source sector of MS could executed in such a way be that the source BS (i.e., the BS of sector CS4 in cell CELL_2) transmits corresponding information to the BS of the target sector CST.

based on this information, will be an initial value to carry out a Searching for the correct current propagation delay searched. This is done by accessing a database in step S2.

In this database, source sectors are stored corresponding propagation delay values. According to this embodiment, a propagation delay initial value is stored for each source sector. An example of the content of such a database is in 4 shown. The values are updated so that the database always provides initial values that are close to the actual propagation delay value. The updating of the propagation delay initial values in the database will be described below.

The database may be located in each BS of each sector or in a Radio Network Controller (RNC). The required memory size is quite low:
Assuming there are 8 possible source sectors, each having a chip delay uncertainty of 512 (if a spread spectrum is used) and a matched filter (MF) length of 32 chips, then the required amount of memory per BS (or sector ) 8 × 512/32 = 128 words.

Therefore the corresponding initial value is taken from the database in step S3 received. Then, in step S4, a search for the correct current propagation delay based on the initial value obtained.

The search strategy used to search the propagation delay value may be, for example, a z-search or an expansion window. Examples of such search strategies are in the 6a to 6e shown. In all figures the uncertainty refers to the delay.

The 6a to 6b are examples of the z search. This search is appropriate if the probability density function is equally distributed over the expected delay (uncertainty). Corresponding 6a the search is started at a starting point at the edge of the interval, whereas the search is commenced accordingly 6b starting from a middle point of the search interval. In both cases, the search is performed continuously over the interval. Corresponding 6c The z search is started from the center, but intermittently, as indicated by the dashed lines.

The 6d and 6e show examples of an extension window. According to this strategy, the search is started from a certain starting point. If the signal is not found at this delay, the next one is checked, and this continues until the search direction is reversed at one point. According to this search, the search interval is increased each time the search direction is reversed. The extension window search strategy is the optimal search strategy if the probability function of the expected delay is normally distributed (with the center as the starting point). An interrupted extension window (as in 6e shown) performs better than the ones in 6d shown continuous expansion window search strategy, if it is known that the probability of detection is always 1 (but this is not usually the case in practice).

The Search can be done using a short matched filter, since the uncertainty of the propagation delay value is small.

To the detection of the actual propagation delay value becomes this value for communication used between the mobile station and the base station, as in Step S5 is displayed.

After that the database is calculated using the detected actual propagation delay value is updated in step S6, which will be described below.

The method described above may be performed by the base station of the target sector CST in cell CELL_3. This base station is in 3 shown schematically. For ease of illustration, only the important for the present embodiment devices are shown.

The base station of the target sector CST is denoted by the reference numeral 1 designated. The base station 1 includes a source cell detector 11 which is adapted to detect the source cell of a mobile station which has just performed a handover operation, ie to execute step S1 described above.

The source cell detected (in the above example, sector CS4 of cell CELL_2) related information becomes an initial value determination means 12 fed. The initial value determination means determines an initial value for the propagation delay search by referring to a database 14 , That is, the initial value determining means performs the above-described steps S2 and S3.

The detected initial value becomes a propagation delay searcher 13 fed. This device performs the above-described search for the propagation delay value (ie, z-search or expansion window). Thus, it serves to execute step S4.

The detected propagation value becomes a communication device 15 fed to a communication with a mobile station 2 via an antenna 16 performs. The communication device 15 uses the detected spread value and thus performs step S5.

It must be noted that the source cell detector 11 , the initial value determination means 12 and the propagation delay searcher 13 can be summarized in a single control device. This control device may include a CPU (central processing unit), a ROM (read-only memory), in which the steps according to 2 are stored as a program and include a RAM (Random Access Memory) as a working memory. Database 14 is preferably a non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or the like.

For those in the database 14 stored propagation delay start values, it is necessary that these initial values be as close to the actual propagation delay values as possible since the search can then be carried out in a very short time. Therefore, the propagation delay initial values should be updated in accordance with the current communication conditions.

In the 1 shown base station 1 includes one to carry out the updating of the database 14 Updated updater 17 , Thus, the actual propagation delay value CPV also becomes the updating device 17 supplied, which can access the database. According to this embodiment, the updating means may be a simple memory access means which can read data and write to a predetermined address. That's why the database is 14 preferably accessible from two sources, ie a non-volatile dual-port RAM or the like.

As an alternative, the updating means 17 can also be integrated into the individual control device described above, so that only needs to be accessed via a port to the database.

According to the present embodiment will update the database by using immediate previously detected propagation delays executed. This means that every time a new propagation delay is detected was this new propagation delay instead of the capture The initial value used for the propagation value is written to the database becomes.

Referring to the example described above, this means that after detecting the current propagation value for a handover from sector CS4 to CST, this current propagation value into the database 14 is written in place of the initial value SPV4 corresponding to the sector CS4.

By This measure the search is always based on the actual immediately before the current one Handover detected propagation delay. Thus, the initial value very close to the current dispersion value.

When Alternative may consider the history of the detected propagation delay become. Such a measure will be for a change of the embodiment described above in the following described.

A predetermined number of past propagation values may be stored and used to generate an initial value therefrom by averaging. To perform this action, the database must be 14 be modified such that for each sector a predetermined number (for example, 5) of propagation delay values is stored. Such a modified database 14 ' is in 5 with five initial values stored for each sector. For ease of illustration, only three sectors are shown. Updating the database 14 ' must be executed so that the oldest propagation delay value is always replaced by the new one. Therefore, the updater must 17 be amended accordingly.

Corresponding this amendment of the preferred embodiment can be avoided that sudden and short-term changes in the communication conditions lead to unrealistic initial values.

According to the above described embodiments the method becomes synchronization in a base station BS carried out. However, the BS is just one example of a network controller. For example, the method may also be implemented in a corresponding base station controller BSC controlling a plurality of BSs or in a mobile services switching center MSC performed which controls a variety of BSC. Such an arrangement is useful, if an existing network is provided with the method according to the invention should. The method is only in a few central network control devices executed Thus, it is not necessary to update each base station. Therefore, you can costs for the updating of a radio network can be reduced.

The The description above and the accompanying drawings merely provide an embodiment of the invention. Therefore, can the embodiments of the invention vary within the scope of the appended claims. It is also possible the embodiments described above (i.e., the preferred embodiment) embodiment and its amendment) combine.

Claims (16)

Method for carrying out a synchronization of a mobile network device ( 2 ) with a network control device ( 1 ) of a current radio network area (CST), comprising the steps of detecting (S1) a source radio network area (CS1 to CS8) from which a handover of the mobile network facility ( 2 ) in the current network area, determining (S2, S3) an initial propagation delay value (SPV1 to SPV8; SPV_1 to SPV_5) based on the detected source radio network area (CS1 to CS8) of the mobile station ( 2 ), and searching (S4) an actual propagation delay value using a search strategy based on the determined initial propagation delay value (SPV1 to SPV8, SPV_1 to SPV_5). Method according to claim 1, wherein initial propagation delay values (SPV1 to SPV8; SPV_1 to SPV_5) for a multiplicity of adjacent sectors (CS1 to CS8) in a database ( 14 ; 14 ' ) get saved. Method according to claim 2, further comprising the step of updating (S6) the database ( 14 ; 14 ' ) with the found actual propagation delay value after performing the search step. Process according to claim 3, being for everyone adjacent sector (CS1 to CS8) has an initial propagation value (SPV1 until SPV8) is stored. Process according to claim 3, being for everyone adjacent sector (CS1 to CS8) have a plurality of initial propagation values (SPV_1 to SPV_5) is used and the average and the distribution of the plurality of initial propagation values (SPV_1 to SPV_5) as basis for the search strategy will be used. Process according to claim 5, where also the distribution of the plurality of initial propagation values (SPV_1 to SPV_5) used as the basis for the search strategy becomes. Process according to claim 1, where the search strategy is an extension window. Process according to claim 1, where the search strategy is a z-search. Network control device of a current radio network area (CST), with a detection device ( 11 ) for detecting a source radio network area (CS1 - CS8), from which a handover of a mobile network device ( 2 ) has been carried out in the current radio network area, a determination device ( 12 . 14 for determining an initial propagation delay value (SPV1 to SPV8, SPV_1 to SPV_5) based on the detected source radio network area (CS1 to CS8) of the mobile station ( 2 ), and a search facility ( 13 ) for searching an actual propagation delay value using a search strategy based on the determined initial propagation delay value (SPV1 to SPV8, SPV_1 to SPV_5). Device according to claim 9, further comprising a database ( 14 ; 14 ' ) are stored in the initial propagation delay values (SPV1 to SPV8; SPV_1 to SPV_5) for a plurality of adjacent sectors (CS1 to CS8), the determining means (12) 12 ) to the database ( 14 ) accesses. Device according to claim 10, further comprising an updating device ( 17 ) for updating the database with the current propagation delay value detected by the searcher. Device according to claim 11, wherein for each adjacent sector (CS1 to CS8) an initial propagation value (SPV1 to SPV8) in the database ( 14 ) is stored. Device according to claim 11, wherein for each adjacent sector (CS1 to CS8) a plurality of initial propagation values (SPV_1 to SPV_5) in the database ( 14 ' ) and the updating device ( 17 ) is set up to use the average of the plurality of initial propagation values (SPV_1 to SPV_5) as the basis for the search strategy. Device according to claim 13, where also the distribution of the plurality of initial propagation values (SPV_1 to SPV_5) used as the basis for the search strategy becomes. Device according to claim 9, where the search strategy is an extension window. Device according to claim 9, where the search strategy is a z-search.